PCNSL is defined as extra-nodal non-Hodgkin lymphoma, which accounts for 2% of all primary CNS tumors. PCNSLs are rare diseases, which commonly occur in the elderly. It is identified that immune evasion and suppressed tumor immune microenvironment were key mechanisms in the pathogenesis of PCNSL. The main pathway was associated with B-cell receptor (BCR) and Toll-like receptor (TLR). BCR signaling pathway was activated by CD79B mutations while TLR signaling axis was activated by MYD88 mutations. They both targeted the Bruton Tyrosine Kinase, leading to CARD11 mutations. In normal B cells, antigen receptor–induced NF-kB activation requires CARD11, a cytoplasmic scaffolding protein. Due to the mutations of CARD11, NFκB activity was amplifying, promoting the growth of PCNSL[5]. Symptoms of patients are diverse according to the CNS lesions area. The most common symptoms are cognitive decline, personality changes and increased intracranial pressure with subacute onset. Focal neurologic signs/symptoms are relatively unusual. Typically, lesions are solitary in 65–80% of cases[6]. It was reported that the 5- and 10-year survival rates for PCNSL are 29.9% and 22.2%. However, in recent years, the survival rate is increasing in the United States population who were immunocompetent[1, 7]. In this study, the patient was 61-year-old with normal immune functions. The primary symptoms involved drowsiness and dizziness, which were atypical and led to delayed diagnosis. A diffusely infiltrating process with involvements of the brainstem, thalamus and hemisphere without discrete were showed in this case. And the patient had poor prognosis.
As clinical prognoses are different, neuroimaging may help to support the diagnosis. In immunocompetent patients, the tumor lesion was isolated and mostly confined to the supratentorial and periventricular location. The most common sites were the cerebral hemisphere (38%), the basal ganglia and thalamus (16%), and the corpus callosum (14%)[8]. Gadolinium-enhanced brain MRI was recommended. It characteristically demonstrated a homogeneously enhancing mass, with surrounding vasogenic edema and no central necrosis. In the MRS, the manifestations of PCNSL include increased choline (cho) peak, moderately decreased NAA peak, slightly decreased creatine (Cr) peak, as well as a significant increase in Lipid and Lac peaks, which indicated neuron damage and increased tumor cell proliferation[9–12]. In this case, MRI showed invasive lesions distributed in not only supratentorial but also infratentorial sites, which was different from previous reports. MRS showed Lac peak increases and NAA peak decreases moderately, which provided us a clue of the malignant tumor.
Although enhanced brain MRI revealed lesions with an enhanced signal, it is a challenge to identify PCNSL and demyelinating diseases. Clinical manifestations and imaging examinations were lack of specificity. Therefore, histopathologic diagnosis is the gold standard for diagnosis of PCNSL, and stereotactic biopsy is currently used. The majority of PCNSL are DLBCL (90%). It separately recognized GCB and non-GCB immunohistochemical subgroups based on the Hans algorithm, which used antibodies to CD10, BCL6, and IRF4/MUM1[13]. It is worth noting that glucocorticoid should generally be avoided preoperatively due to the risk of a nondiagnostic biopsy. As the patient was treated with glucocorticoid pulse therapy before the biopsy, we choose the resection of the cerebellum lesion to improve the diagnostic accuracy. The morphological changes and the result of immunohistochemistry were typical, drawing a conclusion for DLBCL (non-GCB group).